1. Field of the Invention
The invention relates to a hand tool, more particularly to a ratchet screwdriver.
2. Description of the Related Art
Referring to FIGS. 1 and 2, a conventional ratchet screwdriver, as disclosed in Taiwanese Patent Publication No. 00369979, includes a handle 1, a main body 2, two substantially U-shaped pawls 201, two springs 202, an adjustment ring 3, and a ratchet wheel 4. The main body 2 is fixed to the handle 1, and has two parallel insert grooves 203 formed offset from the center of the main body 2. The pawls 201 are respectively inserted into the insert grooves 203. Each of the springs 202 is disposed between one of the insert grooves 203 and the corresponding pawl 201 so as to bias the pawl 201 away from the main body 2. The adjustment ring 3 is sleeved on the main body 2, and has two angularly spaced-apart indentations 302 formed in an inner peripheral face 301 thereof. Each indentation 302 has an inclined guide face 303. The ratchet wheel 4 is sleeved on the main body 2 adjacent to the adjustment ring 3, and has a plurality of teeth 402 formed circumferentially around an inner face of the ratchet wheel 4 to engage one of the corresponding pawls 201. When the adjustment ring 3 is rotated, each pawl 201 is guided by the inclined guide face 303 of the corresponding indentation 302 to change position.
Although the aforementioned conventional ratchet screwdriver can achieve its intended purpose, because only one side of each pawl 201 is meshed with the corresponding tooth 402 of the ratchet wheel 4, meshing forces between the pawls 201 and the corresponding teeth 402 are relatively weak, thereby resulting in an insufficient torque-bearing capacity of the ratchet screwdriver. Further, when the adjustment ring 3 is rotated, the pawls 201 can only move in a straight line relative to the main body 2. This may adversely affect the smooth operation of the adjustment ring 3.
Referring to FIGS. 3 and 4, another conventional ratchet screwdriver, as disclosed in Taiwanese Patent No. M269147, includes a handle 5, an actuator 6 fitted to the handle 5, two pairs of pawls 701 installed on the actuator 6, two springs 702 each disposed between a corresponding pair of the pawls 701, a control ring 8 sleeved on the actuator 6, and a ratchet wheel 9 disposed on one side of the control ring 8. Each of the pawls 701 is provided with a plurality of teeth 701′. The control ring 8 has a plurality of studs 801. The ratchet wheel 9 has a plurality of teeth 901. The teeth 701′ of each pair of the pawls 701 mesh with the corresponding teeth 901 of the ratchet wheel 9 through biasing action of the corresponding spring 702. Hence, when the control ring 8 is rotated, the pawls 701 are pushed by the studs 801 so as to achieve changing of the positions of the pawls 701.
Although the aforementioned conventional ratchet screwdriver can achieve its intended purpose, to ensure that the teeth 701′ of the pawls 701 can mesh accurately with the teeth 901 of the ratchet wheel 9, the pawls 701 are generally made by powder metallurgy, which results not only in high production costs, but also in structurally weak pawls 701. Further, the pawls 701 can only move in a straight line relative to the actuator 6, which may have an adverse effect on the smooth operation of the control ring 8.